Atrial Septal Defects

Heart With Atrial Septal Defects

An Atrial Septal Defect, or ASD, is a hole in the wall between the right and left atria (atrial septum). In the presence of an ASD, blood flows from the higher pressure left atrium to the lower pressure right atrium.

When this happens, the oxygen-rich blood of the left atrium is redirected through the right side of the heart and back to the lungs. The right atrium, right ventricle, and pulmonary artery may enlarge due to the increased blood flow through these structures.

Long-term side effects of an untreated ASD include atrial arrythmias (loss or abnormality of rhythm), ventricular dysfunction, and pulmonary vascular obstructive disease (a condition in which the pulmonary arteries become thickened due to high blood flow). For these reasons, it is preferential to close even small ASDs early in life to prevent complications later in life.

Three Types of ASD

Secundum-Type ASD

Secundum-type ASDs are the most common, comprising approximately 85% of all ASDs. In many cases, infants and young children are asymptomatic and the ASD may not be detected until school age or later. Approximately 20% of secundum-type ASDs close spontaneously in the first year of life. Often, a heart murmur, associated with the increase in blood flow across the pulmonary valve, is the symptom that causes a physician to investigate further. The diagnosis of an ASD is confirmed by echocardiography.

In a secundum-type ASD, the hole is located in the central part of the atrial septum. The methods of treatment for a secundum-type ASD consist of surgical repair or a catheter technique. Options for surgical repair involve suture closure (reserved for small ASDs) or patch closure. The patch material may be a portion of the patients own pericardium (the sac around the heart) or a synthetic material. The catheter technique involves closure of the ASD with a synthetic device that plugs the hole. The device is introduced through a heart catheter which is passed through a vein in the leg that leads up to the heart. Initially, the device is held in place by the natural pressures created within the atria. Over time, the device acts as a framework over which normal tissue grows.

Sinus Venosus ASD

Sinus venosus atrial septal defects constitute 5% to 10% of all ASDs. In a sinus venosus ASD the hole is located in the upper portion of the atrial septum. This type of ASD is often associated with anomalous drainage of the right, upper pulmonary veins. In other words, the pulmonary veins, which normally carry oxygenated blood from the lungs to the left atrium, drain into the right atrium instead. There is no chance for spontaneous closure of this type of ASD. For this reason, surgical repair is necessary for patients with this type of ASD.

Primum-Type ASD

Primum-type ASDs constitute between 5% and 10% of all ASDs. In a primum-type ASD the hole is located in the lower part of the atrial septum. Frequently, abnormalities of one or more heart valves (most often the mitral valve) are associated with this defect. Unlike the secundum-type ASD, symptoms of this type of ASD are seen during early childhood. Surgical repair is the only method of treatment for a primum type ASD since there is no chance of spontaneous closure.

What Is Normal Cardiac Anatomy?

When your child has a congenital heart defect, there's usually something wrong with the structure of his or her heart's structure.

Heart With Normal Cardiac Anatomy

When your child has a congenital heart defect, there's usually something wrong with the structure of his or her heart's structure.

The heart is composed of four chambers. The two upper chambers, known as atria, collect blood as it flows back to the heart. The two lower chambers, known as ventricles, pump blood with each heartbeat to the two main arteries (the pulmonary artery and the aorta). The septum is the wall that divides the heart into right and left sides. The atrial septum separates the right and left atria; likewise, the ventricular septum separates the two ventricles.

There are four valves that control the flow of blood through the heart. These flap-like structures allow blood to flow in only one direction. The tricuspid and mitral valves, also known as the atrioventricular valves, separate the upper and lower chambers of the heart. The aortic and pulmonary valves, also known as the arterial valves, separate the ventricles from the main arteries. Oxygen-depleted blood returns from the body and drains into the right atrium via the superior and inferior vena cavas. The blood in the right atrium then passes through the tricuspid valve and enters the right ventricle.

Next, the blood passes through the pulmonary valve, enters the pulmonary artery, and travels to the lungs where it is replenished with oxygen. The oxygen-rich blood returns to the heart via the pulmonary veins, draining into the left atrium. The blood in the left atrium passes through the bicuspid, or mitral, valve and enters the left ventricle.

Finally, the oxygen-rich blood flows through the aortic valve into the aorta and out to the rest of the body.